Protection of Bridges Subject to Accidental and Intentional Vessel Impact

As part of our transportation infrastructure work, PEC provides consultancy services for the design and protection of bridges subject to accidental and intentional vessel impact. This work includes analysis to calculate loading and structural response consistent with the requirements of the AASHTO Bridge Specifications for accidental impacts. For malicious impact threats, PEC often employs high-fidelity physics based methods for deterministic assessment of structural impact loads and response.

Barge-Bridge Impact in Webbers Falls, Oklahoma

In the United States, vessel impact threats to bridges are established through risk assessment procedures outlined in the AASHTO Bridge Specifications. This process involves a site-specific evaluation of vessel traffic—including both large vessels (tankers) and smaller vessels (tugboats/pushboats)—in addition to environmental conditions such as commonly observed currents and crosscurrents that could contribute to vessel aberrancy. This information is then utilized in conjunction with the bridge geometry to determine collision probabilities associated with each exposed pier and vessel group. Collapse probabilities associated with vulnerable structural components are computed from maximum component resistance levels and impact energy calculations specific to each vessel group. By combining collision and collapse probabilities, an annual frequency of collapse (AF) may be computed for each vulnerable structural component. The summation of these AF values is then compared against permissible limits to assess adequacy of the proposed bridge design.

Current AASHTO procedures governing vessel impact risk assessments have been updated sparingly since their original development in the early 1990s. The University of Florida (UF), working in conjunction with the Florida Department of Transportation (FDOT), recently conducted a series of experimental and analytical investigations specific to barge-bridge impacts with a focus on providing improvements to existing vessel impact analysis and design methods. While at UF working under Dr. Gary Consolazio, current PEC engineer Dr. George Kantrales was involved in several of these studies covering various aspects of the risk assessment process (for more details on previous work, including publicly available research reports, click here). Such efforts included large-scale testing to validate crushing characteristics of barge bows from which peak design loads are computed, numerical studies to assess impact energies of loaded multi-barge tows, and a probabilistic study to recalibrate one of the fundamental terms used in the determination of barge-bridge impact probabilities.

Our familiarity with the AASHTO risk assessment process, the role of our staff in providing recommended improvements to these procedures, and our deep knowledge of impact dynamics and protective design put PEC is in a unique position to provide value-added support to our clients in areas where vessel impact threats are of concern. For more information, please contact George Kantrales.